Elongated working platforms are well known in the art and are commonly used during construction to support workers and equipment at desired elevations. Working platforms of this nature include for example, stationary scaffolding as well as moveable elevating platform assemblies. Although stationary scaffolding is useful, in many instances it is desired to change quickly the elevation of workers and equipment and thus, elevating platform assemblies are advantageous.
One known type of elevating platform assembly is disclosed in U.S. Pat. No. 6,523,647 to Duplessis and assigned to Hydro-Mobile Inc. of L'Assomption, Quebec, assignee of the subject application. This elevating platform assembly comprises an elongated platform that is supported at one end by a mast. A drive mechanism acts between the elongated platform and the mast. The drive mechanism includes a trolley moveable along the mast to which the elongated platform is secured. A motor is mounted on the trolley and drives pinions that cooperate with a rack secured to the mast. In this manner, the elongated platform can be moved upwardly and downwardly along the mast.
Safety is always an issue and so elevating platform assemblies of this nature are provided with emergency brakes to inhibit uncontrolled and/or undesired downward movement of the elongated platforms relative to the masts. For example, many such elevating platform assemblies are provided with emergency brakes that are activated when the rates of descent of the elongated platforms relative to the masts reach an upper threshold rate.
U.S. Pat. No. 6,082,506 to Huang et al. discloses a braking arrangement for an elevating work platform comprising a brake body, a C-shaped receiving device, a brake unit and a brake release handle. The brake arrangement allows only upward movement of the elevating work platform during normal operation. Downward movement of the elevating work platform is permitted only upon actuation of the brake release handle. The braking arrangement also provides an emergency stop in the event of a main cable or winding machine failure.
U.S. Pat. No. 4,531,617 to Martin et al. discloses an overspeed safety braking device comprising an input shaft, a rotary friction brake having a fixed part and a rotary part, a control device and a centrifugal activated structure. The centrifugal activated structure comprises a braking member which rotates with the input shaft when the speed of the input shaft is below an upper threshold speed limit. A weight is pivotally mounted on the braking member. A biasing spring is coupled to the weight member and is arranged to bias the weight member towards the axis of rotation of the input shaft when the speed of the input shaft is below the upper threshold speed limit and away from the axis of rotation of the input shaft when the speed of the input shaft is above the upper threshold speed limit.
Although prior art emergency brakes are satisfactory, improvements in braking mechanisms to ensure quick and reliable braking in an emergency situation are desired. It is therefore an object of the present invention to provide a novel braking device for an elevating platform assembly and to an elevating platform assembly incorporating the same.